1. Field of the Invention
This invention relates to a stably operating pulse combustor and a method for stabilizing the combustion process at a desired location in a Rijke-type pulse combustor. This invention also relates to a pulse combustor adapted to burn either a liquid fuel or a pulverized, solid fuel within a preselected location of the combustion chamber, thereby ensuring that the acoustic pulsations in the combustor are utilized to a maximum beneficial extent to, inter alia, optimize the performance of the combustor.
2. Description of the Prior Art
Although pulse combustors have been generally known for many years, I disclosed in my U.S. Pat. No. 4,529,377 for the first time a pulse combustion apparatus capable of stably burning unpulverized solid fuels. This pulse combustor utilizes the excitation of sound waves to obtain beneficial results. The benefits achieved by this device include increased efficiency of the combustion process, improved heat transfer, and the reduction of pollutants and slagging. As shown in the '377 patent, in order to excite pulsations in a Rijke-type pulse combustor, most of the combustion process energy must be released at a distance of L/4 from the combustor entrance plane, where L is the combustor length. More generally, most of the combustion process energy must be released at a distance of .lambda./8 from the acoustic pressure minimum, where .lambda. is the excited acoustic wavelength and where the acoustic velocity oscillations lead the acoustic pressure oscillations by 90 degrees. In this combustor, it is also required that the flow of gases be directed towards the location of the acoustic pressure maximum immediately downstream of the combustion region.
In Rijke-type combustors it is difficult, however, to attain nearly complete combustion of the fuel over a relatively short distance around the above-specified location on the excited acoustic wavelength. For example, when burning liquid and pulverized solid fuels, the combustion process is often distributed over a significant fraction of the combustor length. When this occurs, only a fraction of the combustion energy is released at the optimum location where it can excite acoustic pulsations, while the remaining fraction of the combustion energy is released beyond the location of maximum acoustic pressure amplitude where it tends to dampen the pulsations. Satisfactory combustor operation cannot, therefore, be attained under such operating conditions. The known literature does not disclose the existence of either a method or apparatus directed to stabilizing the combustion process in a specific volume of a pulse combustor.
Prior pulse combustors and combustion systems are generally described in U.S. Pat. No. 4,529,377 to Zinn, et al.; U.S. Pat. No. 4,699,588 to Zinn, et al.; U.S. Pat. No. 4,770,626 to Zinn, et al.; U.S. Pat. No. 4,642,046 to Saito, et al.: U.S. Pat. No. 4,708,635 to Vishwanath: and U.S. Pat. No. 4,640,674 to Kitchen. These prior art references, however, do not address the problem of decreased efficiency of pulse combustors burning liquid or pulverized solid fuels caused by the combustion process energy being released outside of an optimum combustor location. None of these references provide any method or apparatus for stabilizing the combustion process of liquid or pulverized solid fuels at an optimum combustor location, to attain effective pulse combustion operation.